A preferred method for joining two circularly-ended tubular segments such as pipes or tubes, or projections from other components is to butt their ends together and orbitally weld them. By orbital is meant to apply a flame or arc to their abutment, and rotate the segments past the flame or arc, or rotate the flame or arc around the segments, the latter being the preferred practice. The terms "tube" and "pipe" are used interchangeably in this specification.
The butt-welding of two pipe or tube segments is a primary application of this invention, but it is far from the only one. It is also common to butt-weld fittings and other components such as valves and regulators to a tube or pipe, or to each other. What all of these have in common is a circularly-shaped tubular end, appropriate for making an orbital weld and long enough to be held by the clamp portion of this weld head. Therefore the scope or applicability of this invention is not limited to the welding of tubes or pipes, but is generic to all abutments suitable for an orbital weld.
It is quite common for the orbital welding procedure to be supplemented by special techniques such as shielding with an inert gas, or with mixes of various shielding gases. The objective of the shielding is to protect the molten metal from oxygen, moisture, hydrocarbons, and other contaminants, so that the weld is made entirely of parent metal. It is now known that such impurities are often not merely surface imperfections, but also migrate into the weld itself, which is undesirable. Furthermore, even when the weld is reliable its surface must be cleaned, which can be quite expensive to do.
A considerable inconvenience inherent in known orbital welders is the difficulty of pre-assembling the components precisely in line, and then locating the orbital device squarely on the central axis of the tubes. When this is accomplished the weld can be consistent and true. Otherwise the weld may be faulty.
It is an object of this invention to provide an orbital welding head and clamp assembly into which the tubes can be inserted laterally, the clamp thereafter acting as a precise jig to hold the tubes while the orbital head makes an accurate weld. This welder quickly and accurately receives and holds the components, and quickly and smoothly welds the butted ends together. It may require only one pass, or more than one pass, depending on the welding procedure, which is usually programmed into a computerized power supply.
It is another object of this invention to avoid the tendency of known welders to blow particulates at the weld because, in these known welders the gas is passed through particle-generating components such as gears, brushes and rotors on its way to the weldment. Also, residual contamination often remains in many crevices in known heads, which are dislodged by the gas stream and carried to the weld by the gas. This invention provides the welder with a gas stream which tends to flush particulates away from the weld, rather than toward it, and provides this gas by means of a high purity passage through the fixturing block, or whatever device is used to fixture the components being welded. The gas flow is through the clamp toward the weld region for this purpose. This avoids or at least greatly minimizes particulate contamination of the weld because the gas does not pass through particle-generating regions.
Yet another object of this invention is to provide a physical shield between the weld region and the moving mechanical parts of the weld head to ward off contaminants from that source. This also reduces the volume of the region that must be occupied by the shielding gas.